Redirect visitors to a "site in maintenance" page?

My site is in maintenance(construction). How to redirect visitors to a "site in maintenance" single page?

I heard something about app_offline.htm for ASP.NET.

Is there something similar for PHP?

• I want that every page from "mysite.com" be redirected to "mysite.com/maintenance.php";
• I don't want to do the minimum modification in the existing site pages, ideally no one.

Apache version 2.2.15
PHP version 5.2.13

From serverfault serhio

• In apache with mod_rewrite you can do it easily, just make the first rule something like

  RewriteRule /.* /maintenance.html [L]
  

  If you want to be able to test the site while everybody else sees the maintenance page, you can also add a condition, excluding some IP addresses, e.g.

  RewriteCond %{REMOTE_HOST} ! example.com
  RewriteRule /.* /maintenance.html [L]
  

  From Dan Andreatta

• In Apache with mod_rewrite created a .htaccess file in the root folder containing:

  Options +FollowSymlinks
  RewriteEngine on
  
  RewriteCond %{REQUEST_URI} !/images/mainetnance.png$
  RewriteCond %{REQUEST_URI} !/maintenance.php$
  
  # here filter the developer's IP/
  #RewriteCond %{REMOTE_HOST} !^888\.888\.888\.888
  
  RewriteRule $ /maintenance.php [R=302,L]
  

  From serhio